Hold-down means for convoluted sheathed heater



June 28, 1966 R. DILLS 3,

HOLD-DOWN MEANS FOR CONVOLUTED SHEATHED HEATER Filed Dec. 20, 1965F'lG.l

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INVENTOR.

BY My, m

l-HS ATTORNEY United States Patent 3,258,580 HOLD-DOWN MEANS FORCONVOLUTED SHEATHED HEATER Raymond L. Dills, Louisville, Ky., assignorto General Electric Company, a corporation of New York Filed Dec. 20,1963, Ser. No. 332,037 Claims. (Cl. 219463) The present inventionrelates to electrical surface heating units such as are used withelectric ranges and particularly to a means and method of assembling aconvoluted sheathed heating element to a supporting spider.

It is a general practice today to manufacture metal sheathed heatingelements with a central resistance conductor inserted into a metallicsheath and embedded in a compacted layer of heat conducting,electrically insulating material, such as powdered magnesium oxide. Sucha heating element is wound in the form of a flat coil to define a flatcooking surface on which a cooking vessel or skillet is to be placed forheating. Such a heating coil is supported from below by an underlyingspider that is adapted to hold the turns or convolutions of the heatingcoils in a flat horizontal position in a circular opening in the topcooking surface of the range. Frequently, the convolutions are held inplace by positioning the convolutions in notches or slots in the spiderand flattening the heating coil therein to position and form a rigidattachment thereto. As there are expansions and contractions of theheating element as its temperature is raised and low- .ered,considerable strains can be set up in the metallic sheath which mayresult in buckling or warping of the heating element so that it is nolonger in a flat horizontal position or plane.

Other fastening means that have been utilized in the past are weldedstraps looped under the spider and having the ends of the straps weldeddirectly to the sheath of adjacent convolutions. This technique can behazardous if not properly mastered on a repetitive basis because aninept welder or a poorly designed automatic welding machine might burnthrough the sheath or at least weaken the sheath to a point where itmight fail prematurely during normal use of the surface heating unit.

A third type of hold-down means which has been used extensively is theformation of tabs on the spider which are crimped around theconvolution. This requires that the crimping pressure must be accuratelygoverned otherwise the sheath might be fractured by poor workmanshipduring the crimping operation or due to the expansion and contraction ofthe heating element during normal use. Also, the high operatingtemperature of the sheath in contact with the crimped tabs causeserosion of the tabs so that in time they do not hold the sheatheffectively.

The principal object of the present invention is to provide a design ofa convoluted sheathed heater held to an underlying spider by strap meanswithout using any mechanical bond to the sheath.

A further object of the present invention is to provide a surfaceheating element with thin strap means for holding the element to asupporting spider while allowing slight relative movement between thesheathed element and spider so as not to set up undue stresses thatwould tend to warp the element out-of-fiat when heated.

A further object of the present invention is to provide a simple strapmeans for holding a plurality of convoluted heating elements to asupporting spider so that when replacement is necessary each element maybe replaced separately.

A still further object of this invention is to provide a convolutedsheathed heating element with looped straps which position theconvolutions with respect to the supporting spider so the convolutionsare always spaced apart for good heat transfer conditions.

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The present invention, in accordance with one form thereof, pertains toa resistance type of sheathed heater formed with flat coils orconvolutions for presenting a fiat cooking surface. The heater rests ona supporting spider having generally radial arms. The convolutions areto be held down to the spider at one or more points so as to steady theheating element thereon while permitting the necessary expansion andcontraction of the element during its use. Strap means is locatedadjacent a radial arm of the spider and it has an intermediate portiontightly looped over at least one convolution, while the two end portionsare immovably secured to the arm. Means are also provided to countersinkthe strap means into the sheathed heater so as to present a flat cookingsurface.

My invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing and its scope will bepointed out in the appended claims.

FIGURE 1 is a top plan view of a surface heating unit embodying thepresent invention;

FIGURE 2 is a front elevational View partly in crosssection of thesurface heating unit of FIGURE 1 taken on line 2-2 of FIGURE 1;

FIGURE 3 is a fragmentary view showing a wire member fastening a singleconvolution onto a radial arm of a supporting spider and taken on theline 3 3 of FIG URE 2;

FIGURE 4 is a fragmentary view partly in cross-section showing amodification of this invention wherein a single wire member fastensthree adjacent convolutions to the underlying spider;

FIGURE 5 is another modification of this invention showing a fragmentaryview of a deep-drawn type spider in place of the intersecting metalstrip type spider of FIG- URES 1-4, where the strap means has its twoends fastened to the top surface of the spider;

FIGURE 6 is another view of the modification of FIG- URE 5 with animproved showing of the transverse configuration of the spider taken onthe line 6-6 of FIG- URE 5.

Turning now to a consideration of the drawing, and in particular toFIGURE 1, 10 represents a portion of a top cooking surface whether it bean electric range or a portable electrical appliance or hotplate. Thecooking surface or cooktop 10 includes a circular recess 11 within whichis supported a surface heating unit 12 embodying the present invention.This heating unit 12 includes three main elements; namely, the metalsheathed heating element 13 that is wound into a flat coil or series ofconvolutions, an underlying supporting framework or spider 14, and anencircling trim ring 15 that is associated with the spider forsupporting the spider from the edge of the circular recess in thecooktop, as will be explained in detail hereinafter.

The convoluted heating element 13 is of standard construction in that ithas a central resistance element 9 that is helically woundlongitudinally of the heating element. A suitable electrical insulatingmaterial such as powdered magnesium oxide 16 is packed around theresistance element and the overall assembly is covered with a thin metaltube or sheath 17 The heating unit shown in FIGURE 1 has two coils, aninner coil 19 of small diameter and an outer coil 20 of larger diameter.As an example, this inner coil 19 has four convolutions while the othercoil 20 has only two. Each coil 19 and 20 has a pair of electricalterminals 21 and 22, respectively. The heated portion of each coil stopsin the flat plane of the coil, and the terminals are best described ascold terminals in that they do not include the helical resistanceheater, but instead a rod-like terminal pin (not shown) as is standardin this art. These terminals 21 and 22 are formed downwardly and thenradially in parallel directions at one side 6 of the heating unit forconnection with a suitable terminal block or combined terminal block andhinge means (not shown).

The inner coil 19 is about 4 inches in overall diameter and it is usedfor low heating requirements and for small size cooking utensils, saucepans and the like. The outer coil 20 is about 6 inches in diameter andit is used either alone or in combination with the inner coil for largersized sauce pans and skillets, it being understood that when these twocoils are connected with either rated voltage or 236 volts or one-halfvoltage that many different heating rates or wattages can be obtainedcovering the whole scale of heating conditions from simmer to quickboil. Admittedly, this invention is not limited to any particular sizeof surface heating element but may be used with any of them.

It is necessary to provide some support means beneath the heatingelement because the metal sheath 17 is not so rigid as to preclude thevarious convolutions from moving up and down with respect to each other.Also, it would be undesirable to reinforce the sheath by increasing thethickness or gauge of the metal, because this would tend to slow downthe heating rate by increasing the mass of the sheath and causing slowheat up and cool down periods, and it also would be inefficient from apower usage standpoint. Many different types of support means are usedin this art and two examples are given in the accompanying drawing.FIGURE 1 shows a supporting framework or spider 24 that is formed ofintersecting metal strips 25 and 26 which are set on edge and are shownas two intersecting right angular diagonal plates. A second modificationof spider is shown in FIGURES and 6 of the drawing which will beexplained hereinafter. These intersecting metal strips 25 and 26 form agroup of four radial arms 27, 28, 29 and 30. Various means may be usedfor fastening the two strips together at the center such as welding,riveting or using lanced tabs, but since this fastening means forms nopart of the present invention such means have not been specificallyillustrated. A metal disk 32 of ornamental design is shown fastened overthe center of the spider to serve as an embellishment as wellas apartial closure of the center opening in the coils of the heatingelement. Usually the manufacturers name and/or registered trademark forthe surface unit is imprinted on this disk.

Now that the heating element 12 is resting on the spider 24, some meansmust be provided for supporting the spider from the cooktop 10. In themodification of FIG- URES l4 this support means is exemplified by anannular trim ring that is of generally angular cross-section as bestseen in FIGURE 2 with an inner periphery formed by a vertical rim 34 anda top portion formed by a generally horizontal or slightly downwardlyinclined flange 35. The vertical rim 34 is adapted to fit within thecircular opening 11 in the cooktop, while the top fiange 35 is adaptedto rest upon the edge or periphery of the cooktop opening 11. Suitableslots are formed in the vertical rim 34 in alignment with the radialarms 27-30, and the outer end of each such arm is provided with a tabsuch as 36 in FIGURE 2 that extends into the slot of the trim ring andis supported thereby.

Now that the heating element 13 is resting on the spider 24, and thespider is supported from the trim ring 15, and the trim ring issupported on the cooktop 10, some means must be provided to prevent theheating element 12 from being displaced from the spider in a horizontaldirection. Strap means have been provided so as to have an intermediateportion looped over at least one of the convolutions, while the two endsof the strap are immovably secured to a radial arm of the spider.Specifically in FIG- URE 2, a strap means in the form of a wire member38 of short length is tightly looped over the convolution of thesheathed heater and the two ends of the wire are twisted slightly toextend down fiat along the side of the radial arm 30 of the spider.Various means may be used 4 for immovably securing the two ends of thewire member to the spider. In FIGURES 2 and 3, a pair of slots 39 areformed in the arm 30 and the ends 40 of the wire member are folded andextended through the slots and then folded back on itself in the mannerof a bent tab. Still looking at FIGURE 2, it will be understood thatalternate convolutions are provided with the wire member 38 and thatthese wires are alternately arranged on opposite sides of the radial arm30. Also to be recognized is the location of these Wire straps. They arepositioned adjacent the radial arm 30 that is opposite the terminal ends21 and 22 of the inner and outer coils 19 and 20 of the heating element13. Of course, it is conceivable that the strap means might be locatedover the remaining three arms 27-29 of the spider, but in that case itwould be preferable not to have more than one strap means for a giventurn or convolution in order to allow some freedom of movement of theheating element during the inherent expansion and contraction movementcaused by the heating up and cooling down of the element. It would bedisadvantageous if the strap means extended above the generally flatsurface of the plurality of convolutions. Hence, the area of theconvolution located beneath each strap is countersunk as at 42 as isbest seen in FIGURE 3.

Turning to a consideration of the modification of FIG- URE 4 where thesame elements are identified by the same reference numerals as found inthe first modification of FIGURES 1 and 3, there is illustrated a Weldedtechnique for fastening the ends of a strap means 44 to the radial arm30 of the spider 24. Moreover, the strap 44 is of the multiple type inthat it is looped over a plurality of convolutions; for example, threeconvolutions which, of course, would simplify the assembly operation andlower the cost thereof. Notice that there are raised tabs 46 betweenadjacent convolutions. These tabs serve as spacers to prevent theconvolutions from being drawn together in a bunch by the tension of thestrap 44 and creating an overheated condition which might bring aboutearly failure of the heating element. Similar spacers 46 could be usedwith the modification shown in FIGURES 1-3, where single wire straps areused for the various convolutions. Looking at FIGURE 2 it will benoticed that slight indentations 47 are formed in the radial arm 30beneath the alternate convolutions which are held down by the straps 38.

Now, in turning to the last modification of FIGURES 5 and 6, the firstimportant feature is the difference in the design of the spider 48 whichhas three or more radial arms of inverted channel shape as is best seenin FIGURE 6. This spider is of deep drawn sheet metal constructionhaving radial arms which are not necessarily mechanically fastened tothe trim ring but instead merely rest on a ledge 49 at the bottom of thevertical rim 44 of the trim ring 34. In other words, the spider 48 isloosely supported within the trim ring. Again the top surface of theradial arm is provided with a series of indentations 50 in which theadjacent convolutions are seated, and a strap member 51 of the multipletype is tightly looped over the convolutions and rigidly fastened to thespider by means of bent-over tabs 52 which extend through suitable slotsin the top surface of the spider arm in a manner somewhat similar to thebent tab construction of FIGURE 2. Again, the area of the convolutionsbeneath the strap is countersunk as at 42 in FIGURE 6. Of course, itwill be appreciated that instead of a multiple strap 51, single strapsfor single convolutions could be used.

Having described above several modifications of the invention of a novelhold-down means for a sheathed heater it will readily be apparent tothose skilled in this art that I have provided a positive hold-downmeans where the coils are always held snugly against the spider withoutthe use of crimped spider tabs, peened sheathed portions or strapmembers that are welded directly to the sheath from below. The variouscoils or convolutions are free to expand in diameter when heated. Thisallows the convolutions to remain fiat. Primarily, no mechanical bond ismade to the sheath nor is any excessive mechanical pressure exerted bythe use of crimped or peened holding means. Moreover, since the variouscoils of the heating element may be individually tied down to thespider, they may be removed separately within the home by the applianceServiceman rather than having to replace the entire heating unit. Also,since the straps are formed of such fine wire, the cost is relativelyunimportant and the strap can be made of expensive high temperatureresistant metal such as Incoloy which will better withstand corrosionand erosion.

Modifications of this invention will occur to those skilled in this arttherefore it is to be understood that this invention is not limited tothe particular embodiments disclosed but that it is intended to coverall modifications which are within the true spirit and scope of thisinvention as claimed.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electrical heating unit comprising a convoluted sheathed heater,the convolutions of which are disposed in a single plane for defining afiat cooking surface, a supporting framework in engagement with theunderside of the heater, the framework having spacer means between atleast some of the convolutions for holding them apart and strap meansfor holding the convolutions to the framework, said strap means havingan intermediate portion looped over at least one convolution and a pairof end portions immovably secured to the underlying framework, theconvolution being indented beneath the strap means for lowering thestrap means beneath the level of the flat cooking surface.

2. An electrical surface heating unit comprising a convoluted sheathedheater, the convolutions of which are disposed in a plane for defining aflat cooking surface, a supporting spider in engagement with theunderside of the heater, the top surface of the spider having raisedportions between at least some of the adjacent convolutions for holdingthem apart, and strap means for tying down the convolutions to thespider, said strap means having an intermediate portion looped over atleast one convolution and the two end portions immovably secured to theunderlying spider, whereby no mechanical bond is made between the strapmeans and the sheath.

3. An electrical surface heating unit comprising a convoluted sheathedheater, the convolutions of which are disposed in a plane for defining afiat cooking surface, a supporting spider having generally radial armson which the heater is rested, the heater having at least two terminalswhich extend beneath the heater at one side thereof, and strap means fortying down the convolutions to the spider, said strap means beinglocated adjacent a radial arm of the spider diagonally disposed from theterminals of the heater, said strap means including at least one smallgauge wire with an intermediate portion tightly looped over at least oneconvolution and the two end portions thereof immovably secured to theunderlying arm of the spider, the portion of the convolution beneath thelooped wire being countersunk to receive the wire beneath the topcooking surface of the heater.

4. A method of attaching a generally fiat metal sheathed heating elementto a spider having supporting arms; comprising, the steps of indentingthe top surface of at least one of the arms, seating the heating elementacross the indentation, countersinking the portion of the elementlocated within the indentation, and tightly looping a wire member overthe countersunk portion of the element, and rigidly fastening the twoends of the wire member to the underlying arm of the spider, whereby thewire member does not protrude above the flat surface of the heatingelement.

5. In a method of attaching a convoluted sheathed heater to a supportingspider having radial arms; comprising the steps of countersinkingcertain intermediate portions of the heater in the area overlying theradial arms, tightly looping a short wire member over each countersunkportion, and rigidly fastening the two ends of the wire member to theunderlying arm of the spider.

References Cited by the Examiner UNITED STATES PATENTS 2,357,150 8/1944Vogel 219463 2,662,157 12/1953 Vallorani 219463 2,881,302 4/1959Ammerman 219-463 2,943,178 6/ 1960 Aldons 219-463 3,031,735 5/1962Jepson 29-1555 3,032,861 5/1962 Foster 29155.5 3,042,785 7/1962 Hanson2l9463 RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

1. AN ELECTRICAL HEATING UNIT COMPRISING A CONVOLUTED SHEATHED HEATER,THE CONVOLUTIONS OF WHICH ARE DISPOSED IN A SINGLE PLANE FOR DEFINING AFLAT COOKING SURFACE, A SUPPORTING FRAMEWORK IN ENGAGEMENT WITH THEUNDERSIDE OF THE HEATER, THE FRAMEWORK HAVING SPACER MEANS BETWEEN ATLEAST SOME OF THE CONVOLUTIONS FOR HOLDING THEM APART AND STRAP MEANSFOR HOLDING THE CONVOLUTIONS TO THE FRAMEWORK, SAID STRAP MEANS HAVINGAN INTERMEDIATE POR-